Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Most images of black holes are illustrations. Here’s what our telescopes capture

vox.com

Post reply on HN
Print view View original

21–30 of 167 posts

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#21

Post by saagarjha »

podiki wrote: post #15
booleandilemma wrote: post #5

If nothing can escape black holes how is it they “spew” things?

They also (are believed to, based on famous calculations by Hawking) radiate like a black body with a temperature related to their mass. And this leads to them losing mass over time, eventually evaporating. (Leaving what is a subject of much debate.)

I believe the "spew" that booleandilemma was referring to were the twin perpendicular "jets" that black holes often seem to eject, for which the explanation is probably some sort of angular momentum/near miss close to the event horizon sort of thing.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#22

Post by short_sells_poo »

ars wrote: post #16
podiki wrote: post #12

Earlier quoted context omitted.

Regarding your last point: that depends on your reference frame. From the outside it does appear to take "forever" to get into a black hole, but if you were the one falling in...it happens much quicker, certainly not taking an infinite amount of time.

That's true. But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. (I'm less sure about this paragraph, but I believe that) An object falling in also never sees a black hole, since the other things falling in are dilated relative to him, so there's still not enough mass to make a black hol…

You seem to misunderstand the way an event horizon works. From the infalling object's (and the hole's) reference frame, the object crosses the event horizon in finite time and falls into the singularity. It is only from an observer's perspective that the object never seems to cross the horizon.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#24

Post by oevi »

Black holes are an excellent example for so called "cognitive metaphors".

Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass.

This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the black hole".

I think it is really interesting how these cognitive metaphors can sometime limit our ability to think about a problem, because they often restrict the properties of the described thing to the properties of the analogy.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#25

Post by ars »

short_sells_poo wrote: post #22
ars wrote: post #16

Earlier quoted context omitted.

That's true. But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. (I'm less sure about this paragraph, but I believe that) An object falling in also never sees a black hole, since the other things falling in are dilated relative to him, so there's still not enough mass to make a black hol…

You seem to misunderstand the way an event horizon works. From the infalling object's (and the hole's) reference frame, the object crosses the event horizon in finite time and falls into the singularity. It is only from an observer's perspective that the object never seems to cross the horizon.

No, that's exactly what I understand.

But we don't care about the infalling object. We care about the observer, because any infalling object initially is an observer, and because we (us humans) are observing the black holes.

Since from an observers POV nothing can actually fall into the black hole, no black hole can form.

The fact that an infalling object reaches the black hole makes no difference to us. Because of time dilation, we can observe no black holes. So our telescopes will never see a black hole.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#26

Post by orf »

Reminds me of one of my favorite moments[1] in Red Dwarf:

> Well, the thing about a black hole - its main distinguishing feature - is it's black. And the thing about space, the colour of space, your basic space colour, is black. So how are you supposed to see them?

1. https://www.quotes.net/show-quote/66989

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#27

Post by dragonwriter »

ars wrote: post #16
podiki wrote: post #12

Earlier quoted context omitted.

Regarding your last point: that depends on your reference frame. From the outside it does appear to take "forever" to get into a black hole, but if you were the one falling in...it happens much quicker, certainly not taking an infinite amount of time.

That's true. But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. (I'm less sure about this paragraph, but I believe that) An object falling in also never sees a black hole, since the other things falling in are dilated relative to him, so there's still not enough mass to make a black hol…

> But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place.

They only take an infinite time to fall in once a black hole has formed; OTOH, unless I misunderstand, the time would asymptotically approach infinity up to that point, which seems to have a similar effect.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#28

Post by teamonkey »

ars wrote: post #25
short_sells_poo wrote: post #22

Earlier quoted context omitted.

You seem to misunderstand the way an event horizon works. From the infalling object's (and the hole's) reference frame, the object crosses the event horizon in finite time and falls into the singularity. It is only from an observer's perspective that the object never seems to cross the horizon.

No, that's exactly what I understand. But we don't care about the infalling object. We care about the observer, because any infalling object initially is an observer, and because we (us humans) are observing the black holes. Since from an observers POV nothing can actually fall into the black hole, no black hole can form. The fact that an infalling object reaches the black hole makes no difference to us. Because of t…

> Since from an observers POV nothing can actually fall into the black hole, no black hole can form.

The event horizon isn't really a physical boundary in that sense. It's the mathematical boundary at which, according to general relativity, a particle must have velocity equal to the speed of light in order to escape. A density change inside the star can change the size and shape of that boundary without things falling into it in the usual sense.

In the same way, a density wave can 'travel' faster than the speed of sound (or light) in a medium because the wave is a mathematical construct that emerges from a physical situation.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#29

Post by westoncb »

oevi wrote: post #24

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the b…

I think this is something that deserves much greater general awareness. I think by default we're pretty unaware of the kind of analogizing/metaphoring that takes place when we conceptualize anything—but it's completely pervasive. I see it as a kind of subtle 'dust on the lens' of the microscope which we use to observe things generally. It's an (in a certain sense) inescapable artifact due to the fact the we conceptualize with a definite thing with its own properties and quirks and limitations, which is the human brain. Anyway, I see it as a kind of 'bias' (best I can think of atm, but that term isn't really broad enough to capture the idea) which we could watch for and in doing so make gains in objectivity.

Edit: also, another way of looking at it is: when we express any concepts in some concrete form, the particular representation we choose (and we have to choose something) brings its own baggage along with it. And, subsequently, we end up reasoning off of the baggage rather than the thing in itself.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#30

Post by saiya-jin »

ars wrote: post #25
short_sells_poo wrote: post #22

Earlier quoted context omitted.

You seem to misunderstand the way an event horizon works. From the infalling object's (and the hole's) reference frame, the object crosses the event horizon in finite time and falls into the singularity. It is only from an observer's perspective that the object never seems to cross the horizon.

No, that's exactly what I understand. But we don't care about the infalling object. We care about the observer, because any infalling object initially is an observer, and because we (us humans) are observing the black holes. Since from an observers POV nothing can actually fall into the black hole, no black hole can form. The fact that an infalling object reaches the black hole makes no difference to us. Because of t…

You seem to be fixed too much on theory, and not (indirectly observed) reality.

The article is very light on hard facts, and doesn't show a single picture of gravitational lensing for example - much more obvious that something not visible with very strong gravity is in path of photons from background.

Relativity theory (proven countless of times in last 100 years) covers this topic very extensively, black holes are a direct result of crossing certain gravitational threshold and can't be avoided.

I think what you describe as an 'issue' is same as racer overtaking another, coming 1/2 meter behind, then 1/4, 1/8th etc. This goes into infinity, so in theory overtaking should never happened (cca infinite sum of finite numbers should be infinity, sorry for the lack of proper english math expressions). Yet in reality it does, and simple arithmetic solve this (forgot the exact name for it, but it's max high school level).

Post reply on HN